Researchers have observed the valley Hall effect (VHE) in monolayer molybdenum disulfide (MoS₂) transistors. The VHE is a new valley degree of freedom (DOF) in 2D crystals, which allows electrons to exhibit a Hall effect without an external magnetic field. This effect is controlled by the helicity of circularly polarized light, which preferentially excites electrons into a specific valley. The observed VHE is consistent with theoretical predictions and is absent in bilayer devices due to restored crystal inversion symmetry. The VHE opens new possibilities for using valley DOF as an information carrier in next-generation electronics and optoelectronics. The study shows that monolayer MoS₂, with a staggered honeycomb lattice structure, is inversion asymmetric, leading to effective magnetic fields in different valleys. This results in a valley Hall effect, where electrons from different valleys move in opposite directions perpendicular to the drift current. The VHE is analogous to the spin Hall effect, with valley-polarized carriers replacing spin-polarized electrons. The experiment involved shining circularly polarized light on a Hall bar device to break time reversal symmetry, creating a valley polarization. A finite anomalous Hall voltage was observed, with its sign controlled by the light's helicity. The magnitude of the Hall effect was consistent with theoretical predictions, and the results were validated by comparing experimental data with the theoretical model. The study also examined the effect of photoexcitation on the Hall response, showing that the A and B resonances of monolayer MoS₂ are influenced by the incident photon energy. The results demonstrated that the VHE is sensitive to the polarization of light and that the anomalous Hall conductivity depends on the carrier density imbalance between the two valleys. The findings confirm the presence of a photoinduced anomalous Hall effect (AHE) in monolayer MoS₂ under on-resonance, circularly polarized excitation, supporting the interpretation that the signal originates from the VHE. The results highlight the potential of valley DOF in future electronics and optoelectronics, with implications for both fundamental physics and emerging technologies.Researchers have observed the valley Hall effect (VHE) in monolayer molybdenum disulfide (MoS₂) transistors. The VHE is a new valley degree of freedom (DOF) in 2D crystals, which allows electrons to exhibit a Hall effect without an external magnetic field. This effect is controlled by the helicity of circularly polarized light, which preferentially excites electrons into a specific valley. The observed VHE is consistent with theoretical predictions and is absent in bilayer devices due to restored crystal inversion symmetry. The VHE opens new possibilities for using valley DOF as an information carrier in next-generation electronics and optoelectronics. The study shows that monolayer MoS₂, with a staggered honeycomb lattice structure, is inversion asymmetric, leading to effective magnetic fields in different valleys. This results in a valley Hall effect, where electrons from different valleys move in opposite directions perpendicular to the drift current. The VHE is analogous to the spin Hall effect, with valley-polarized carriers replacing spin-polarized electrons. The experiment involved shining circularly polarized light on a Hall bar device to break time reversal symmetry, creating a valley polarization. A finite anomalous Hall voltage was observed, with its sign controlled by the light's helicity. The magnitude of the Hall effect was consistent with theoretical predictions, and the results were validated by comparing experimental data with the theoretical model. The study also examined the effect of photoexcitation on the Hall response, showing that the A and B resonances of monolayer MoS₂ are influenced by the incident photon energy. The results demonstrated that the VHE is sensitive to the polarization of light and that the anomalous Hall conductivity depends on the carrier density imbalance between the two valleys. The findings confirm the presence of a photoinduced anomalous Hall effect (AHE) in monolayer MoS₂ under on-resonance, circularly polarized excitation, supporting the interpretation that the signal originates from the VHE. The results highlight the potential of valley DOF in future electronics and optoelectronics, with implications for both fundamental physics and emerging technologies.